DescriptionRhinoderma darwinii is a relatively small frog (males 22-28 mm, females 25-31 mm). It has a pronounced, fleshy proboscis, which gives the head a triangular appearance. Tympana are indistinct. The skull is weakly ossified. Forelimbs and hindlimbs are relatively long and slender. Webbing is moderate between toes I and II, and II and III, less developed between toes III and IV, and lacking between toes IV and V. A metatarsal tubercle is present but not as large as that of the related species Rhinoderma rufum. Brooding males have enlarged vocal sacs, due to the sacs containing developing embryos. Coloration is highly variable, with the dorsum being either uniform brown (tan, brown, or reddish brown), uniform green (pale or dark), or some combination of brown and/or green with variable patterns. The underside is black and white, with large blotches (Crump 2003; Duellman and Trueb 1986).

Larvae lack external gills, a spiracle, a beak, and denticles, indicating they are not free-living. Larvae also lack interdigital membranes and digital tubercles on the hind legs. The caudal fin is poorly developed (Jorquera et al. 1972).

This species occurs in central and southern Chile, and Argentina. In Chile it occurs from the province of Maule south to the province of Aisen, up to 1500 m in elevation. In adjacent Argentina it is found in the provinces of Neuquen and Rio Negro (Crump 2003). Rhinoderma darwinii is found in temperate and austral forests, along cool
(5-21 degrees C) and wet stream banks of slowly moving streams (Penna and Veloso 1990; Cooper et al. 1978; Crump 2003), as well as forest bogs (IUCN 2006).

Life History, Abundance, Activity, and Special BehaviorsDuring the colder months, Rhinoderma darwinii shelters under cover of logs or moss (Crump 2003). This species is mainly diurnal, and often basks in sunlight (Crump 2003). Despite being primarily diurnal, males call at night as well as during the day (Crump 2003). Vocalization is most prevalent throughout the breeding season (November through March; Crump 2003). The call is a rapid "piiiip, piiiiip, piiiiip, piiiiip" (Crump 2003). Individuals were observed giving an average of 2.5 calls/minute, at an average frequency of 2550 Hz (Penna and Veloso 1990). Calls are composed of 2 to 3 notes, with the total call lasting between 580 and 1700 msec (Penna and Veloso 1990).

In captivity, and probably also in the wild, the male leads the female to a sheltered site, where courtship is conducted. After some time, the female moves underneath the male. Amplexus is loose, rather than the male gripping the female tightly (Crump 2003).

This species is a direct developer, without free-living larvae (Jorquera et al. 1982), and has a very unusual form of parental care. In each terrestrial clutch, deposited in the leaf-litter, there are about 40 large (4 mm), unpigmented eggs
(Duellman and Trueb 1986; Jorquera et al. 1972). Clutch size in the far south of the range may be smaller (3-7 eggs; Crump 2003). After the male has fertilized the eggs, he remains in close proximity. When the larvae have reached the stage where they can wriggle inside the eggs (about 20 days post-oviposition), the male takes the embryos up into his vocal sac, where they hatch into tadpoles about 3 days later (Cei 1962; Jorquera et al. 1982). As many as 19 embryos have been found within a male's vocal sac (Busse 1970); it is not known what the maximum is.

After hatching, larval development and metamorphosis take place within the vocal sac of the male parent (Jorquera et al. 1982). This post-hatching period of development lasts for about 50-70 days (Jorquera et al. 1982; Crump 2003). The male not only shelters the tadpoles but nourishes them via viscous secretions within the vocal sac (Goicoechea et al. 1986). Within the vocal sac, the tadpole absorbs paternal nutrition via the skin, and yolk from the egg (Goicoechea et al. 1986). By stage 11, yolk is depleted (Jorquera et al. 1982). In addition, the intestinal epithelium has differentiated by this stage, so that the tadpole is now also able to ingest parental nutritious secretions via the mouth and absorb it via the digestive system (Goicochea et al. 1986). At the end of metamorphosis the froglets move from the male's vocal sac into the mouth, and emerge from the mouth (Jorquera et al. 1982).

Only one other species of frog (Rhinoderma rufum) broods embryos within the male's vocal sac. Although this species has not been been experimentally confirmed to transport substances from the paternal circulation to the larvae, it has the same specialized secretory structures within the vocal sac epithelium as does R. darwinii. However, in Rhinoderma rufum the embryos are retained for a much shorter time within the vocal sacs, and complete development as free-living larvae, outside the male. In Rhinoderma rufum, the larvae develop keratinized jaws (unlike in R. darwinii). In addition, the intestinal epithelium matures much earlier in development (stage 2 in R. rufum vs. stage 11 in R. darwinii). The larvae of R. rufum are expelled from the male's vocal sac at stage 3 to feed and finish development in an aquatic environment, unlike those of R. darwinii, which complete development wholly within the male's vocal sac (Jorquera et al. 1982).

This frog has the unusual defensive strategy of playing dead when threatened; it rolls over on its back and remains motionless. If it is near a stream when frightened, it may jump into the stream and float in the water on its back (Crump 2003).

Rhinoderma darwinii consumes insects and other small invertebrates, using a sit-and-wait predation strategy (Crump 2003).

Trends and ThreatsMost of the range is within Chile. Rhinoderma darwinii is most abundant on the archipelago, where there is little habitat disturbance, and in some southern Chilean localities. In other parts of the range within Chile, populations are declining or have vanished entirely, in some cases due to deforestation or replacement of native trees with non-native pine or eucalyptus, but in other cases from unknown causes. This species is rare in Argentina (IUCN 2006).

Relation to HumansIt can be found in open areas around human habitation, primarily in swampy areas or near slowly running streams (Crump 2003).